SHARKS AND SKATES. 85 



have the same square appearance, with long filaments at the corners, as was described 

 on a preceding page, for Scyllium. The eggs are not infrequently thrown up upon 

 the beaches, and have the common name sea-purses. In England the term ' shark-bar- 

 rows ' is in common use, from their diminutive resemblance to a hand-barrow. The de- 

 velopment of the rays has been studied by several, but the paper by Jeffries Wyman 

 is the best known in America. In the earlier stages the young skate is much like a 

 shark, and the enormous development of the pectoral fins, and the assumption of the 

 ray form, does not occur until nearly the time of hatching. 



Most curious of all the rays are the saw-fishes (Peistid^) so abundant in the tropical 

 seas. In general appearance, they closely resemble the Pristophoridae among the sharks ; 

 they have a shark-like body, while' the snout is horizontally flattened and projects far 

 beyond the mouth. On the edges of this snout, stout teeth are inserted, so that the 

 resemblance to a saw is all but complete. The saw-fishes are among the most formidable 

 of the order, for this singular weapon places all the other large inhabitants of the sea 

 at their mercy. With it, the saw-fish cuts and slashes, tearing off pieces of flesh, or rip- 

 ping open the abdomen of its opponent. The saw is sometimes very large, reaching 

 a length of six feet, and a breadth of twelve inches. The teeth of the jaws are so 

 small as to unfit the animals for a predacious life, were it not for the saw. The pieces 

 which-this tears off are readily swallowed. The saw-fish is a great enemy of the whale. 



Five sjjecies of the single genus Pristis are known ; distinguished among 

 each other, among other points, by the number of teeth in the saw. P. pectinatits, 

 with twenty-five to twenty-eight pairs of teeth, occasionally occurs on our southern 

 coasts and in the Gulf of Mexico, occasionally ascending the lower Mississippi. P. 

 antiquoruni occurs in Lake Nicaragua as well as in the tropical oceans. The 

 saw-fishes are viviparous, though but little is known of their development. The saw 

 and its teeth are developed before the young leaves its mother's body. The flesh of 

 the saw-fish is coarse and unpalatable, though it is occasionally used as food in time 

 of need. The shagreened skin is put to the same uses as that of sharks. 



The RhixobatiDjE are also somewhat shark-like, the anterior portion of the body 

 not showing that excessive development to be found in the other families of the order, 

 and the pectoral rays are not continued to the snout. The tail is large and strong, 

 and bears two dorsals and a well-develojjed caudal fin. All bring forth their young 

 alive. It contains some fifteen or twenty species, inhabiting the warmer seas. Our 

 fauna contains four species, all belonging to the genus Phinohatus, three on the west 

 coast, and one in the waters around Florida. They are not well known. 



The interest in the family Toepedinid^ centres in their electric powers. As we 

 shall see farther on, they are not the only vertebrates capable of generating electricity, 

 and, in fact, they are less celebrated in this line than are the electric eels of South 

 America. Still their powers in this respect are not to be despised. The torpedos 

 have a broad, smooth, disc-liko body, from which arises a stout tail, with a longitudinal 

 fold on either side; usually a dorsal, strengthened by rays, is present, while a caudal 

 always occurs. 



The electrical organ consists of two large masses of hexagonal prisms, looking 

 much like the comb of the honey bee, placed one on either side, between the head and 

 the pectoral fins, and covered by the integument. The prisms are vertical, and each 

 is divided by transverse partitions into a number of cells. Lining the inside of the 

 cells is a layer of connective tissue, which bears the nerves and blood vessels ; inside 

 of this a nucleated epithelium, and within this a clear, transparent, almost jelly-like 



